堆——优先队列

堆——优先队列
堆是一种特殊的完全二叉树（父节点都比子节点大或小）

顺便说一下二叉树 如果共有n个节点 则树的高度为logN 父节点是第k个节点 则左儿子是2k 右耳子是2k+1

最小堆 父节点都要比子节点小 根的值一定是最小的 其他的值的顺序无法确定 最大堆相反
优先队列

• 思想：由最小堆或者最大堆实现 并通过堆排序保持队列的有序性 模拟队列的结构
• 函数：pq.pop( ) pq.push(）pq.size( ) pq.top( )

priority_queue<int,vector<int>,greater<int> >pq; //最小堆 最小的元素在栈顶priority_queue<int,vector<int>,less<int> >pq;    //等同于priority_queue<int>pq; struct node{    int x, w;    bool operator < (const node &a) const  //只能重定义<     {        return w < a.w;    }};

题目：B - Fence Repair &&F - The kth great number
F - The kth great number
Xiao Ming and Xiao Bao are playing a simple Numbers game. In a round Xiao Ming can choose to write down a number, or ask Xiao Bao what the kth great number is. Because the number written by Xiao Ming is too much, Xiao Bao is feeling giddy. Now, try to help Xiao Bao.
Input
There are several test cases. For each test case, the first line of input contains two positive integer n, k. Then n lines follow. If Xiao Ming choose to write down a number, there will be an ” I” followed by a number that Xiao Ming will write down. If Xiao Ming choose to ask Xiao Bao, there will be a “Q”, then you need to output the kth great number.
Output
The output consists of one integer representing the largest number of islands that all lie on one line.
Sample Input
8 3
I 1
I 2
I 3
Q
I 5
Q
I 4
Q
Sample Output
1
2
3

Hint
Xiao Ming won’t ask Xiao Bao the kth great number when the number of the written number is smaller than k. (1=

#include <iostream>#include <cstdio>#include <queue>using namespace std;int main(){    int n,k;    while(scanf("%d %d",&n,&k)!=EOF)    {        getchar();        priority_queue<int,vector<int>,greater<int> >q;        int i,t;        char c;        for(i=0;i<n;i++)        {            scanf("%c",&c);            if(c=='I')            {                scanf("%d\n",&t);                if(i<k)                q.push(t);                else if(t>q.top())                {                    q.pop();                    q.push(t);                }            }            if(c=='Q')            {                printf("%d\n",q.top());                getchar();            }            //printf("%c\n",c);        }    }    return 0;}